1. Field of the Invention
The present invention relates to an internal combustion powered hydraulic engine in which the amount of hydraulic fluid that is pressurized is selectively altered during the combustion cycle.
2. Description of the Prior Art
In an era of growing concern for environmental pollution, decreasing reserve of fossil fuels and increasing gasoline prices, the efficiency of energy conversion in automobile and other engines is of extreme importance. The shortcomings of the conventional internal combustion engine in these areas are well known. Limitations inherent in the fundamental engine design result in less than optimum efficiency. Incomplete combustion necessitates complex smog control devices.
These inefficiencies result in part from the mechanical arrangement in a conventional reciprocating internal combustion engine. Each piston is connected via a connecting rod and crankpin to a crankshaft which itself delivers the output power. The speed of rotation of this crankshaft thus dictates the rate at which combustion must occur. The crankpin pressure angle dictates the points of acceleration, deceleration and stopping of the associated piston. During combustion, the burning gases must expand and exert force against the piston under conditions of acceleration dictated by the crankshaft and crankpin. Yet the optimum efficiency gas expansion rate seldom will be equal to the increasing cylinder volume dictated by the piston motion. Similarly, the piston must stop at the top and bottom limits of the crankpin travel. However, at the bottom limit, the gases in the cylinder may still be expanding, and could provide additional useful work. Inertial forces are absorbed at these top and bottom limits by the connecting rod and crankpin; this energy is lost.
An object of the present invention is to provide an engine in which the combustion rate is not dictated by mechanical crankshaft limitations and in which inertial forces are recovered as useful work. More complete combustion and more efficient energy conversion is achieved by using an internal combustion assisted hydraulic engine.
A known hydraulic drive internal combustion engine is disclosed in the U.S. Pat. No. 2,661,592 to Bright. In that engine, the piston of an internal combustion chamber is connected via a bell crank to the plunger of a single hydraulic cylinder. During the combustion cycle, hydraulic fluid in the cylinder is pressurized. The pressurized fulid is used to drive a liquid turbine that turns an output shaft. Some of the pressurized fluid is stored by an accumulator which provides pressurized fluid to the turbine when the hydraulic cylinder is not being pressurized. This stored pressurized fluid also is used to return the piston in the combustion chamber to the position at which gas is compressed and ready for combustion. To this end, the plunger in the hydraulic cylinder also is connected to another piston that is subjected to the force of the pressurized hydraulic fluid during the fuel compression cycle.
In engines of the type just described, the output fluid pressure level is limited by the resistive force of the output accumulator. The force exerted by the combustion chamber at the end of its power stroke must be at least equal to this relatively fixed accumulator resistive force in order to move additional pressurized output hydraulic fluid into the accumulator. As a result, if the hydraulic chamber is connected directly to such an accumulator or like pressurized storage arrangement, the pressure in that accumulator must remain at the minimum valve obtained near the end of the cyle. Otherwise, the higher pressure from the accumulator would exert a counter-force on the hydraulic piston that would prevent further compression and perhaps stop the engine. As a result, high pressure at the beginning of the power stroke cannot be obtained, resulting in a substantial loss of efficiency.
Another object of the present invention is to provide an internal combustion assisted hydraulic engine in which the output hydraulic fluid pressure level is maintained at or near the maximum value available at the beginning of the power stroke. To this end, a variable displacement fluid system is employed in which the amount of displaced hydraulic fluid decreases as the forces acting on the piston decrease. As a result, the output hydraulic fluid varies in volume, but is maintained at a high pressure level. Much higher conversion efficiencies are achieved than are possible with prior art engines.
Another shortcoming of prior art hydraulic engines relates to misfiring. If a misfire occurs, there is no force to drive fluid into the output accumulator. Misfire detection circuitry and special valves are required in prior art engines to allow cycling without the combustion assist. A further object of the present invention is to provide a hydraulic engine which does not require special detection systems to compensate for misfiring.
Another limitation of prior art hydraulic engines results from their use of large input and output fluid accumulators in which the pressure cannot be changed quickly. As a result, such engines must operate with equal power strokes. In contrast, it is an object of the present invention to provide a hydraulic engine capable of operating with strokes of different power, and utilizing a small output accumulator to smooth the pressure and volume variations of a few strokes. This allows the inventive engine to operate under different conditions of acceleration, deceleration and output pressure over a short period of time. As a result the engine is capable of operating efficiently at different speeds, rates of acceleration and deceleration, and under differing power loads. This is particularly useful in automobile applications where a wide variety of operating conditions are encountered.